CVE-2025-38509 is a vulnerability in the Linux kernel's mac80211 wireless subsystem where VHT operating mode notifications for unsupported channel widths below 20 MHz (such as 5 MHz and 10 MHz) were not properly rejected. This could cause malformed notifications to trigger a kernel warning (WARN_ON) due to invalid input. The issue has been addressed by rejecting unsupported widths early in the processing of VHT opmode notifications.